Apparatus and method for controlling the application of plastic material to casting surfaces of sheeting machines



Sept. 7, 1954 1 APPARATUS AND METHOD FOR CONTROLLING THE APPLICATIONFiled March 16, 1953 G F NADEAU ETAL 2688,155

OF PLASTIC MATERIAL TC CASTING SURFACES 0F SHEETING MACHINES 2Sheets-Sheet l GALE F NADEAU WAL rm P. WHITE INVENTORS amwx A IATTORNEYS Sept. 7, 1954 G. F. NADEAU ET AL 2,638,155

APPARATUS AND METHOD FOR CONTROLLING THE APPLICATION OF PLASTIC MATERIALTO CASTING SURFACES OF SHEETING MACHINES Filed March 16, 1955 2Sheets-Sheet 2 GALE i WADE AU WALTE/EN RN WIgZTE E T0 04m! Q1flTTOR/VEYS Patented Sept. 7, 1954 APPARATUS AND METHOD FOR CONTROL-LING THE APPLICATION OF PLASTIC MA- TERIAL T CASTING SURFACES OFSHEETING MACHINES Gale F. Nadeau and Walter R. White, Rochester, N. Y.,assignors to Eastman Kodak Company, Rochester, N. Y., a corporation ofNew Jersey Application March 16, 1953, Serial No. 342,326

7 Claims. 1

This invention relates to an improved method and apparatus for castingan evaporative-type dope on a surface to form sheeting. Such sheetingmay be used for packaging, for film base, and for other purposes.

In this art it has always been diflicult to form sheeting which isperfectly smooth and of an accurate thickness throughout, largelybecause relatively slight air disturbances or vibrations may tend toruin the sheeting by causing wrinkles, waves, or the like, in thesurface of the sheeting before it sets. While some of theseimperfections may smooth out before setting, it is usually difficult orimpossible to prevent a permanent deforming of the sheet.

Our invention is particularly directed to a method and apparatus forovercoming these and other difficulties and to provide a means whichreduces or entirely eliminates vibrations in the fluid dope beingdeposited upon a dope-receiving surface by a suitable hopper. It hasbeen recognized that it is desirable to reduce eddy and other aircurrents about the dope as it passes from a hopper, as is indicated inPatent 2,592,319, Casting Apparatus for Film Support or Sheeting, G. F.Nadeau and A. M. Glasoe, granted April 8, 1952. It has not, however,been recognized that beneficial results could be obtained by reducingthe usual air currents on that side of the hopper from which the castingsurface approaches to have the dope laid on the wheel. As is pointed outin the above patent, the usual type of casting machine employs anendless surface, such as the periphery of a wheel or a belt, which isprovided with an accurate, smooth surface and which moves constantlypast the hopper so that a plastic sheet may be spread on the surface,set or dried until it is self -supporting, at which time the sheet maybe stripped from the casting surface. Where wheels are used, they arefrequently of large diameter, such as, for instance, from 10 to 18, andan enclosure is built about the wheel to carry off solvent vapors and tocontrol the temperatures. Because of the nature of these enclosures andthe large size of the machine, it is difiicult if not impossible, tobuild up a casing which can be streamlined to such an extent that theair will follow exactly the desired path. Ducts, supporting rollers, andeven the sheet being formed all contribute to the difficulty ofobtaining smooth even air circulation.

An object of our invention is to overcome the difficulties above pointedout. Another object of our invention is to provide a method of breakingup air currents atthe portion of the machine where they appear to be themost harmful. A further object of our invention is to provide a bafliingsystem which causes the air to follow a path in which it will notmaterially affect the dope being laid on the casting surface. A stillfurther object of our invention is to provide an apparatus in which noadditional air circulation, other than that already present in thecasing of the apparatus, is required to produce the desired effects.Still another object of our invention is to provide a means ofprotecting the head of dope passing from the hopper to the castingsurface against unwanted circulation of air. A still further object ofour invention is to prevent a thin layer of air which is believed tofollow the surface of the casting member from passing into the bed ofdope being laid on the wheel. Other objects will appear from thefollowing specification, the novel features being particularly pointedout in the claims at the end thereof.

The invention, both as to its organization and its methods of operation,together with additional objects and advantages thereof, will be bestunderstood from the following description of the specific embodimentswhen read in connection with the drawings in which:

Fig. l is a greatly simplified view showing a casting wheel in elevationand certain parts in section of a typical embodiment of our invention.It may be pointed out in this figure that the scale of the parts isdeformed in order to better illustrate the invention;

Fig. 2 is a top plan View showing a portion of the side walls in sectionof an improved air baiile constructed in accordance with, and embodyinga preferred form of, our invention and showing on an enlarged scale thebaffle shown in Fig. l. Unessential details of the apparatus are omittedin this View;

Fig. 3 is a fragmentary detail section, parts being shown in elevationof a second embodiment of our invention. Here again the scale of theparts is distorted to better illustrate th invention; and

Fig. 4 is a, part side elevation and part section showing schematicallya slightly dilferent embodiment of our invention.

We found that one of the disturbing air currents which affects thelaying of a head of plastic material on a casting surface is a thinlayer of air which appears to follow the casting surface as it passestoward the hopper. While it had been previously recognized that air onthe freshly laid layer of dope could readily disturb its surface, it wasnot thought that the air on the opposite side of the bead passing fromthe hopper to the casting surface was materially affected, particularlysince the distance of the coating blade to the casting surface was oftenquite small, such as, for instance, .05. It is to be understood thatthis figure is by way of example since, of course, the distance from theblade to the casting surface is altered for various differentthicknesses of sheeting.

Referring to Fig. 1 showing a preferred form of our invention, a wheel Imay be mounted on trunnions 2 and may be turned in any well-knownmanner. In this view, the wheel turns in a clockwise direction so that acasting surface 3, which preferably is highly polished, may move beneatha hopper 4 having casting blades 5 and 6. These blades may be adjustedin known manners to and from each other and the casting surface 3. Aspointed out above, the hopper blade 5 may be spaced from the castingsurface a distance of .030 to 1.000". This hopper may contain a fluid orplastic dope l of the evaporative type which may flow down between thehopper blades 5 and 5 to the casting surface, after which it may becarried around the wheel and stripped off after setting and reaching aselfsupporting stage. It may be received from the casting surface 3 bypassing it about a roller 8 and leading it away from the casting surface3 and over suitable rolls 9, I0 and l I. There is a casing broadlyindicated at l6 having an air inlet [1 in the top and an opening 18through which the set sheet 20 passes out and over a guide roller l 2.To prevent solvent vapors from collecting in casing l6, air may becirculated to draw them away from the casting surface 3 and the sheetlaid thereon. There is a partition 2| leading from the hopper 4 to anair duct 22 from which air is drawn through the duct 23 by suitablemeans, such as an air pump 24. The solvent vapors may be reclaimed bypassing through the pipe 25 to a suitable recovery apparatus and ifdesired, the purified air may be recirculated to duct 28. There is apartition 26 dividing the air duct 22 into two sections, one of which2'! passes around the periphery of the wheel I and leading to an airduct 28 into which air passes to practically encircle the wheel. Thereis an opening 29 into the chamber I 5 through which the sheeting passesbefore it is stripped from the wheel over roller 8. Thus, the chamber I6is subjected to air currents which cannot pass smoothly in the shortestpath or in a streamline manner through the casing from the inlet I! toair exit [3 connected by duct [4 to exit duct 25. The air must passabout the edges of the sheeting and various other parts. of the casingand machine such as roller supports, ducts, hopper, and the like, and itis therefore broken up in variable speed components.

In order to prevent these air currents and others from reaching thestream of dope 3| passing downwardly from the hopper blades to thecasting surface 3even though this distance is exceedingly smallwe haveprovided an air baffle 32. This air baille, as best shown in Fig. 2, maylie between side walls 33 and 34 of the casing and it may be, andpreferably is, supported by such walls.

It may comprise a box-like frame consisting of end pieces 35 and 36mounted on the walls 33 and 34 with a plurality of partition plates 31extending between the end members and front and back frame members 38and 39. The plates or slats 31, 38 and 39 are preferably spaced apart toprovide flue-like openings 40 between the slatlike members and, tomaintain these in correct alignment, we prefer to provide a series ofrods 4| with spaced members 42 so that the air baffle plates will beheld in position. Different numbers of baffle plates may be used and wehave found that from three to six or more is usually satisfactory,although this may depend in part on the amount of air circulation whichmust be dispersed.

For average materials, the air circulation in the chamber l6 may be from300 to 1500' per minute. It is believed, however, that a principal causeof disturbance of the bead 3| is a thin layer of air which follows thesurface of the casting wheel or belt.

As will be noted from Fig. 1, the baffle plates 31, 33 and 39 may beapplied in parallel relationship with the bottom edges spaced from thewheel from, for instance, .055" to .065. This spacing is not toocritical, and may be varied. In fact, it sometimes does vary slightlyeven between the air bafiles because the slats or baffle plates are madein a generally rectangular form for convenience, and such a bafile doesnot, of course, exactly follow the curvature of the casting surfacewhere a wheel is used. However, where the wheel may be, say, 18' indiameter, the curvature does not depart far from a straight line in adistance of perhaps 3 or 4". By way of example, such a baflle may be,for instance, 3 or 4 wide, and perhaps 4" high, and the length of thebaffle will preferably extend from wall to wall on each side of thecasting surface.

It may be also desirable but not essential to provide another air bafliestrip 43 which may have a plush or soft cloth 44 mounted along thebottom edge, as indicated. Such a strip may be spaced some distance fromthe casting surface 3 as, for instance, .020". Thus, with the air ballieplates and the air baffle strip 43 mounted as shown in Fig. 1, any layerof air following the casting surface must pass beneath the narrowopenings between these members and the casting surface. It has beenfound that the reduction in the velocity of air around the dope castingunit with the construction above described is very beneficial. The airbaflle generally shows a material up-draft between the first and secondair baffles counting the baffles from left to right. Between subsequentbaffles, there appears to be only a slight up draft, indicating theescapement of air that had managed to pass under the first one or twobaffles.

It is very difficult to determine exactly what occurs with thisconstruction, but the resulting effect is quite obvious-that there isfar less disturbance with the labyrinth air baffle than is presentwithout it. Where there is considerable air circulating in variousdirections, it is particularly difficult to describe accurately theexact path the air takes with such an apparatus as there are so manycontributing factors which may vary somewhat at different times.Nevertheless, a labyrinth-type baffle has been quite successful.

In Fig. 3, there is a slightly different embodiment of our invention inwhich the hopper is mounted on rails 5| and 52 and the hopper blades 53and 54 lay the plastic coating 55 on a casting surface 56 of a wheel 57.Here, there i a casing plate 58 with a second plate 59 extending overthe top of that surface of the wheel upon which the plastic material hasbeen flowed, and this plate may be attached or taped at 60 to plate 58.In this form of the invention, there may be a suction chamber 6| withasuction pipe 62 leading to an air evacuating apparatus so that air inthe chamber 6| may pass out through the suction box 64. The chamber 6|will be held under a somewhat different pressure than the pressure in acasing, similar to casing I6 shown in Fig. 1, and this pressure may befrom 3 to 10" of water. In this case, there is an air baffle strip 65having a bottom edg 66 spaced from the wheel a distance of perhaps .020,and the labyrinth or air baffle may consist of a series of spaced plates61 with flues 68 extending between the baffle plates. Thus, air whichmay tend to follow the surface 56, either due to the turning of thewheel 51 or to the suction in chamber 63, in passing under labryrinthbaffle and air baffle strip is broken up and is at least partiallypassed up through the fines 68 so that very little passes into thechamber 6| and so that the vacuum line 62 may draw off air evenly fromthe bead 69 of plastic dope being laid upon the wheel. In other words,the air in the chamber 6| will not be disturbed by eddy currents, eventhough the air is being constantly drawn out by the vacuum apparatus.Presumably, this causes an even pressure on the length of the bead 69and prevents uneven air currents from reaching this bead and,consequently, wrinkling it. If desired, the air baffle strip 65 may bemade a part of the air baiiles or may be entirely omitted.

Fig. 4 is still another embodiment of our invention wherein the castingsurface ID is a polished belt mounted on wheels ll with a hopper 12above the belt. The hopper has blades 13 and [4 so that a bead 75 ofmaterial can be laid on the belt. In this instance, there is an airbaffle 16 and, if desired, an air baffle strip 1'! which may be spacedfrom the casting surface as in the embodiments shown above.

It should be stressed that under the dope hopper, it is necessary tominimize to the greatest extent possible any movement of air whether theair stream be more or less uniform and streamline or whether it beturbulent and made up of eddy currents. It is only by maintaining afairly static air condition under the hopper and near the dope hopperorifice that slugging of the dope on the hopper blades can be prevented.The use of th labyrinth bafiie in addition to preventing air flow up thesurface of the wheel and under the dope hopper also has the virtue ofaccomplishing this result without contacting the wheel surface. Themechanism by which a multiple slot labryrinth type baffle works isgenerally considered to be a result of frictional loss of energy in theair stream as a result of its flow up through the narrowly spacedmembers of the bafiie. Because of the number of them and their relativecloseness, the air velocity is decreased due to typical viscous energyconsiderations. It follows, therefore, that there will be some exhaustof air from the tops of the bafile under most conditions of operation.It is conceivable that with very high impingement velocities against thebaffle, some down draft or aspirator effect at the first or second slotcould be realized. This situation, however, under our conditions ofoperation and with the air velocities involved does not exist.

The air baffle or labyrinth is quite simple and it may be made of wood,metal or other suitable material. It may be desirable to cover thebafiie plates with material which can be readily laundered or cleanedas, for instance, linen sheeting or the like.

While we have illustrated a preferred form of our invention, it isobvious that many changes will suggest'themselves to those skilled inthe art, and we contemplate as within thescope of our invention all suchchanges as may come within the scope of the appended claims.

Having thus described our invention, what we claim is new and desire tosecure by Letters Patent of the United States is:

1. Apparatus for casting plastic sheet material comprising a movablecasting surface, a hopper for depositing a uniform layer ofevaporativetype plastic dope on the casting surface, a chamber throughwhich air is circulated over at least a portion of the casting surfacebefore it reaches the hopper, means for controlling the circulating airmoving over the casting surface and toward the hopper comprising aplurality of closelyspaced bafile plates extending across the castingsurface out of contact with the casting surface but lying close thereto,said bafile plates extending in a direction away from the castingsurface to provide narrow flue-like spaces between the baffle plates toresist eddy currents in the air adjacent the hopper whereby an evenlayer of plastic dope may be spread on the casting surface. 1

2. Apparatus for casting plastic sheet material of the type defined inclaim 1 characterized in that the movable casting surface is carried bya wheel and in that the baffle plates may extend away from the wheelcasting surface in a generally radial direction.

3. Apparatus for casting plastic sheet material of the type defined inclaim 1 characterized in that the baflle plates are parallel to eachother, in that at least one baffle plate extends radially away from thecasting surface of the wheel, and in that the fines between the bafileplates are many times the height of the separation of the plates.

4. A method of minimizing irregularities in spreading a thin even layerof plastic dope upon a moving casting surface comprising passingcirculating air over the casting surface adjacent an area where theplastic dope is applied to the casting surface and dividing a portion ofthe circulating air into a plurality of thin parallel streamssubstantially as wide as the casting surface and as it approaches thedope applying area to prevent substantial amounts of air from movingtoward the application area at which the plastic dope is applied.

5. A method of minimizing irregularities in spreading a plastic dope ofan evaporative-type on a casting surface comprising circulating airabout the area where the dope is applied to a casting surface, anddividing a portion of the air into a plurality of parallel streamsextending across the casting surface as it approaches the dope-applyingarea to prevent eddy currents of air from contacting flowing dope.

6. A method of minimizing irregularities in spreading a plastic dopesheeting on a casting surface comprising circulating air thereabouts,restricting air circulation in a direction toward an area in which fluiddope is applied to the casting surface by dividing the air into aplurality of parallel layers directed at substantially right angles tothe casting surface and adjacent the area where the dope is applied tothe casting surfaces to prevent eddy currents from contacting theflowing dope to the casting surface.

7. A method of minimizing irregularities in spreading a plastic dopesheeting on a moving 2,688,155 I 7 a casting surface comprisingcirculating air therecarried along by the casting surface or other airabouts to carry off solvent vapors, said casting currents from cominginto contact with and desurface tending to carry a layer of air alongwith forming the dope flowing to the casting surface.

the surface as it moves, restricting air circulation in a directiontoward an area in which fluid 5 References Cited in the me of thlspatent dope is applied to the casting surface by divid- UNITED STATESPATENTS ing the air into a plurality of parallel layers ad- Number Namet jacent to and leading away from the casting sur- 2,051,201 DavidsonAug. 18, 1936 face as it approaches the area where the dope 2,201,747Staudt May 21, 1940 is applied thereto to prevent eddy currents, air 102,226,186 Van Derhoef Dec. 24, 1940

